Reverse genetics permits the recombinant expression and manipulation of RNA viruses in cell culture. It is a powerful tool in virology and vaccine manufacture because it allows rapid production of recombinant viruses (including reassortants) and/or their mutation. The method involves transfecting host cells with one or more expression constructs that encode the viral genome and isolating the virus from the cells. For example, references 1 and 2 describe a method in which the influenza genomic RNA is expressed in canine cells using the canine pol I promoter. Other sources have reported the expression of influenza genomic RNA in human cells using the human pol I promoter
One significant drawback of the methods of the prior art is that pol I promoters are highly species specific. For example, it has been reported that the human pol I promoter is active only in primate cells [3], and similarly that expression in canine cells would require the canine pol I promoter. Thus, where a virus needs to be grown in a cell line for which the endogenous pol I promoter has not been characterized, it has been necessary to use two different cell types for rescuing and growing the virus. However, it is desirable to avoid the use of multiple cell lines as this has the advantage, for example, that competing culture selection pressures can be avoided. The use of a single cell line for all steps of vaccine production also facilitates regulatory approval. Thus there is a continued need in the art to provide alternative methods for practising reverse genetics.